Two soldiers died and three others received toxic burns on November 12 during a chemical spill at the Plesetsk Cosmodrome in northwestern Russia.

A Russian Defense Ministry official said the accident occurred while the men were cleaning a nitrogen fuel tank. The ministry added that the accident was caused "by the officers' failure to follow safety procedures."

The cosmodrome -- which is about 800 kilometers north of Moscow -- was built during the Soviet era and is now Russia's only alternative to the Baikonur Cosmodrome that Moscow leases from Kazakhstan.